Elevator cabs presently include a motor driven fan mounted centrally on the cab roof. The motor driven fan typically includes a suitable electric motor that is operable when connected across a 110 VAC power source to drive a fan blade in the ventilating system to draw air from the elevator shaft for flow through the elevator cab and back to the shaft. Such elevator ventilation systems can include an emergency ventilation system that has a separate DC motor driven fan connected to a separate DC power source when the main AC power source fails. The DC motor driven fan is operable to provide a back-up ventilation when the AC motor driven fans are rendered inoperative because of main power failure.
Present elevator ventilation systems for normal and emergency operation, therefore require two separate air flow delivery systems, one including an AC motor driven fan and the other including a separate DC motor driven fan and wherein the separate air flow delivery systems are selectively operated in accordance with whether or not a main AC power supply has failed.
In many other systems for ventilating elevator cabs only one motor driven fan is connected to the regular AC power source. The air discharge from each such motor driven fan is directed through a single outlet hole in the center of the elevator cab roof. Most elevators, however, have a drop ceiling that restricts the flow of such discharge through the elevator compartment and outlet hole.